What do we mean by "Astronomical Night"

Dear astro-friends,

Allow me to ask a very “newbie” question - and please apologize if this has already addressed in the forum (didn’t find an answer to my question, hence this topic).

I am currently writing my dragscript - so far so good - but I am confused with the “astronomical night” option. What do we mean exactly by “astronomical night”, is it when it’s dark enough to start off with the sequence ? Or is it simply “dusk” ?

I am asking because I would like to have my sequence start automatically when it’s dark enough. However, I don’t want to use the “wait until…”.

I thank you in advance for your kind support.

My best regards from Switzerland.

It is defined as the sun having set to 18 degrees below the horizon and often considered as true night time i.e. it wont get much darker. Up here at 52 degrees north we have a significant period where there is no Astronomic Darkness during summer months.

For practical purposes I use Astronomic Darkness with an offset of 30 minutes prior before starting imaging. I tend to Have Voyager connect everything up and cool the camera at Wait Until Dusk and then Park the mount and Wait Until Astronomical Darkness -30 before running the first sequence.


You can also try nautical night with Sun at -12 degrees.

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Thank you both for your kind support ! Really helpful.


Yep i am also from 52, in drag script you can specify Nautical Night and I use that because there is no astronomical night in the summer. So for starting all items in the drag script work oke, but what do you specify for your end of the sequence. I used Absolute time and i cacluated the nautical night for each run. Due to this issue i add this calculation in my OCS see below

It would be handy to have in the sequence also the options end sequence at nautical night. How do you solve this one?

Thanks in advance chris

I normally exit when the last sequence target reaches a specific lower altitude limit (about 35 degs for my setup) but then have a catchall repeat until a specific time. At this time of year I may end up throwing the last few frames


I understood about the altitude, but i don’t understand the second part you explained. do i understand it correctly that you use also use immediately Start and end at Absolute time you specify



Take a look at the sample DragScript’s. I do much the same but have a sequence constraint to exit if <30degrees but then have a repeat until say 4:30 in DragScript for the last block. If it’s getting light at 4:30 I may then loose a few subs but heh.

I have a somewhat limited horizon so tend to image multiple targets over multiple nights so have to arrange targets from 30 degrees east to 35 degrees west. Takes a bit of planning and a spell of bad weather can scupper things but Voyager reliably takes care of it.


I recently purchased a SQM-LE and have been taking measurements for the past few months. I’ve found that once the sun goes down below an altitude of -14.5, my sky brightness saturates, and no additional gains can be made in terms of sky brightness. It would be awesome if we could have a trigger in the sequence or timing in Dragscript based on solar altitude, and not time offset from astronomical dusk.

No Gabe , offset its ok.

All the best

Can DragScript use the sky brightness number reported by a sky monitoring station? Not sure if that variable is available. The problem with winter vs summer ‘night’ and using an offset for nautical night has to do with the rate of darkness change. In winter darkness changes very fast, but in summer darkness changes very slowly. The rate of change depends on your latitude, larger extremes for the more northerly latitudes. This means the offset would have to be changed often when moving from winter to summer and vice versa. A sky brightness variable would help with this.


As long as the equipment has an ASCOM driver then you should be able to get the sky brightness into Observing Conditions and update a variable to it and make DragScript decisions based on the value. My Eagle 4 does it easily.

On a practical point sky brightness here varies quite considerably from night to night and through the night itself so it might not be granular enough to make decisions on.

If the forecast is good, I setup target sequences in the afternoon and let it run. Viking powers things up and the sequences run as it gets dark. It’s the work of moments to change the end time.